1. Field of the Invention
The present invention relates to a process for preparing aldehydes by hydroformylation of olefinically unsaturated compounds, in particular olefins, catalyzed by an unmodified metal catalyst derived from a metal of groups 8 to 10 of the Periodic Table of the Elements, which process is carried out in the presence of cyclic carbonic esters as solvents.
2. Discussion of the Background
The reactions of olefin compounds, carbon monoxide and hydrogen in the presence of a catalyst to form the aldehydes having one more carbon atom are known as hydroformylation (oxo process). Catalysts used in these reactions are frequently compounds of the transition metals of groups 8 to 10 of the Periodic Table of the Elements, in particular compounds of rhodium and of cobalt. In comparison with catalysis by cobalt compounds, hydroformylation using rhodium compounds generally offers the advantage of higher chemo-selectivity and regioselectivity and is therefore usually more economically attractive.
The rhodium-catalyzed hydroformylation is usually carried out using complexes comprising rhodium and compounds of group 15 of the Periodic Table of the Elements, preferably trivalent phosphorus compounds, as ligands. For example, compounds from the classes of phosphines, phosphites and phosphonites are frequently used as ligands. An overview of the hydroformylation of olefins may be found in B. CORNILS, W. A. HERRMANN, “Applied Homogeneous Catalysis with Organometallic Compounds”, Vol. 1&2, VCH, Weinheim, N.Y., 1996.
Terminal olefins can easily be reacted in the presence of phosphine-modified rhodium catalysts. On the other hand, internal olefins and especially internal highly branched olefins require strongly activating ligands such as phosphite ligands. In addition, “naked” or unmodified rhodium has also been found to be well suited in the case of olefins which are difficult to hydroformylate. These catalysts comprise one or more metal species which are formed under hydroformylation conditions from a metal salt in the absence of modifying ligands. For the purposes of the present patent application, modifying ligands are compounds which contain one or more donor atoms of group 15 of the Periodic Table of the Elements. However, modifying ligands do not include alkoxy, carbonyl, hydrido, alkyl, aryl, allyl, acyl or alkene ligands, nor the counterions of the metal salts used for catalyst formation, e.g. halides such as fluoride, chloride, bromide or iodide, acetylacetonate, carboxylates such as acetate, 2-ethylhexanoate, hexanoate, octanoate or nonanoate.
Modifying ligands for the purposes of the present patent application are ligands which contain donor atoms from group 15 of the Periodic Table of the Elements, for example nitrogen, phosphorus, arsenic or antimony, in particular phosphorus. The ligands can be monodentate or polydentate, and in the case of chiral ligands, either the racemate or one enantiomer or diastereomer can be used. Particularly important examples of phosphorus ligands are phosphines, phosphinines, phosphinanes, phosphine oxides, phosphites, phosphonites and phosphinites.
Examples of phosphines are triphenylphosphine, tris(p-tolyl)phosphine, tris(m-tolyl)phosphine, tris(o-tolyl)phosphine, tris(p-methoxyphenyl)phosphine, tris(p-fluorophenyl)phosphine, tris(p-chlorophenyl)phosphine, tris(p-dimethylaminophenyl)phosphine, ethyldiphenylphosphine, propyldiphenylphosphine, t-butyldiphenylphosphine, n-butyldiphenylphosphine, n-hexyldiphenylphosphine, c-hexyldiphenylphosphine, dicyclohexylphenylphosphine, tricyclohexylphosphine, tricyclopentylphosphine, triethylphosphine, tri(1-naphthyl)phosphine, tri-2-furylphosphine, tribenzylphosphine, benzyldiphenylphosphine, tri-n-butylphosphine, tri-i-butylphosphine, tri-t-butylphosphine, bis(2-methoxyphenyl)phenylphosphine, neomenthyldiphenylphosphine, the alkali metal, alkaline earth metal, ammonium or other salts of sulfonated triphenylphosphines such as tris(m-sulfonylphenyl)phosphine, (m-sulfonylphenyl)diphenylphosphine; 1,2-bis(dicyclohexylphosphino)ethane, bis(dicyclohexylphosphino)methane, 1,2-bis(diethylphosphino)ethane, 1,2-bis(2,5-diethylphospholano)benzene [Et-DUPHOS], 1,2-bis(2,5-diethylphospholano)ethane [Et-BPE], 1,2-bis(dimethylphosphino)ethane, bis(dimethylphosphino)methane, 1,2-bis(2,5-dimethylphospholano)benzene [Me-DUPHOS], 1,2-bis(2,5-dimethylphospholano)ethane [Me-BPE], 1,2-bis(diphenylphosphino)benzene, 2,3-bis(diphenylphosphino)bicyclo[2.2.1]hept-5-ene [NORPHOS], 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl [BINAP], 2,2′-bis(diphenylphosphino)-1,1′-biphenyl [BISBI], 2,3-bis(diphenylphosphino)butane, 1,4-bis(diphenylphosphino)butane, 1,2-bis(diphenylphosphino)ethane, bis(2-diphenylphosphinoethyl)phenylphosphine, 1,1′-bis-(diphenylphosphino)ferrocene, bis(diphenylphosphino)-methane, 1,2-bis(diphenylphosphino)propane, 2,2′-bis-(di-p-tolylphosphino)-1,1′-binaphthyl, O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane [DIOP], 2-(diphenylphosphino)-2′-methoxy-1,1′-binaphthyl, 1-(2-diphenylphosphino-1-naphthyl)-isoquinoline, 1,1,1-tris(diphenylphosphino)ethane, and/or tris(hydroxypropyl)phosphine.
Examples of phosphinines include 2,6-dimethyl-4-phenyl-phosphinine, 2,6-bis(2,4-dimethylphenyl)-4-phenylphosphinine and also further ligands described in WO 00/55164. Examples of phosphinanes include 2,6-bis(2,4-dimethylphenyl)-1-octyl-4-phenylphosphinane, 1-octyl-2,4,6-triphenylphosphinane and further ligands described in WO 02/00669.
Examples of phosphites are trimethyl phosphite, triethyl phosphite, tri-n-propyl phosphite, tri-i-propyl phosphite, tri-n-butyl phosphite, tri-i-butyl phosphite, tri-t-butyl phosphite, tris(2-ethylhexyl)phosphite, triphenyl phosphite, tris(2,4-di-t-butylphenyl) phosphite, tris(2-t-butyl-4-methoxyphenyl) phosphite, tris(2-t-butyl-4-methylphenyl) phosphite, tris(p-cresyl) phosphite. Further examples are sterically hindered phosphite ligands as are described, inter alia, in EP 155 508, U.S. Pat. No. 4,668,651, U.S. Pat. No. 4,748,261, U.S. Pat. No. 4,769,498, U.S. Pat. No. 4,774,361, U.S. Pat. No. 4,835,299, U.S. Pat. No. 4,885,401, U.S. Pat. No. 5,059,710, U.S. Pat. No. 5,113,022, U.S. Pat. No. 5,179,055, U.S. Pat. No. 5,260,491, U.S. Pat. No. 5,264,616, U.S. Pat. No. 5,288,918, U.S. Pat. No. 5,360,938, EP 472 071, EP 518 241 and WO 97/20795. Among the sterically hindered phosphites, mention may be made of the triphenyl phosphites which are substituted by 1 or 2 isopropyl and/or tert-butyl substituents, preferably in the ortho position relative to the phosphite ester group. Further bisphosphite ligands are mentioned, inter alia, in EP 1 099 677, EP 1 099 678, WO 02/00670, JP 10279587, EP 472017, WO 01/21627, WO 97/40001, WO 97/40002, U.S. Pat. No. 4,769,498, EP 213639 and EP 214622.
Examples of phosphonites are methyldiethoxyphosphine, phenyldimethoxyphosphine, phenyldiphenoxyphosphine, 6-phenoxy-6H-dibenz[c,e][1,2]oxaphosphorin and their derivatives in which all or some of the hydrogen atoms are replaced by alkyl or aryl radicals or halogen atoms and ligands as described in WO 98/43935, JP 09-268152 and DE 198 10 794 and in the German patent applications DE 199 54 721 and DE 199 54 510.
Customary phosphinite ligands are described, inter alia, in U.S. Pat. No. 5,710,344, WO 95 06627, U.S. Pat. No. 5,360,938, JP 07082281. Examples are diphenyl(phenoxy)phosphine and its derivatives in which all or some of the hydrogen atoms are replaced by alkyl or aryl radicals or halogen atoms, diphenyl(methoxy)phosphine, diphenyl(ethoxy)phosphine, etc.
In industrial hydroformylation, the reaction product, unreacted starting material and catalyst are usually separated by distillation. The hydroformylation is therefore carried out in the presence of a high-boiling solvent so that the work-up by distillation gives a high-boiling catalyst-containing fraction which can be recirculated to the process. In many continuous industrial hydroformylation processes in which rhodium catalysts are used, the high-boiling mixtures formed as by-product in the hydroformylation are used as solvents, as described, for example, in DE 2 062 703, DE 2 715 685, DE 2 802 922, EP 017183.
In addition to the high boilers, it is possible to use inert organic liquids (DE 3 126 265) and reaction products (aldehydes, alcohols), aliphatic and aromatic hydrocarbons, esters, ethers and water (DE 4 419 898) as solvents. In GB 1 197 902, saturated hydrocarbons, aromatics, alcohols and n-paraffins are used for this purpose.
The addition of one or more polar organic substances in the hydroformylation process is disclosed, for example, in WO 01/68248, WO 01/68249, WO 01/68252. For the present purposes, polar substances are substances from the following classes of compounds: nitrites, cyclic acetals, alcohols, pyrrolidones, lactones, formamides, sulfoxides and water.
In the hydroformylation of relatively long-chain olefins (C≧6), the separation of the catalyst from the reaction product and possibly unreacted starting materials by distillation requires high temperatures and low pressures. Sometimes considerable decomposition of the rhodium-containing catalyst takes place during this distillation, regardless of whether or not an additional ligand has been used. This results in the catalyst being lost to the process, which has a drastic adverse effect on the economics of the process.
The unmodified rhodium catalysts are found to be particularly unstable. The prevailing opinion among those skilled in the art is that the mononuclear complex HRh(CO)3 is, in the absence of modifying ligands, the species which is active in the hydroformylation. The complex HRh(CO)3 is stable only at temperatures below 20° C. and under high pressure (N. S. Imyanitov, Rhodium Express, (1995), 10/11, 3–64) and is in equilibrium with a binuclear species which itself is not active but serves as a reservoir of active catalyst (E. V. Slivinskii, Y. A. Rozovskii, G. A. Korneeva, V. I. Kurkin, Kinetics and Catalysis (1998), 39(6), 764–774) (A. R. El'man, V. I. Kurkin, E. V. Slivinskii, S. M. Loktev, Neftekhimiya (1990), 30(1), 46–52). Hydroformylation-inactive clusters of increasing molecular weight are formed from the binuclear rhodium carbonyl complex. Under the conditions of an intensive hydroformylation reaction, the formation of the low molecular weight clusters is reversible. It has been demonstrated that clusters up to Rh4(CO)12 can be regenerated. The stabilization of the active species under hydroformylation conditions has likewise been able to be demonstrated (Yu. B. Kagan, Y. A. Rozovskii, E. V. Slivinskii, G. A. Korneeva, V. I. Kurkin, S. M. Loktev, Kinetika i Kataliz (1987), 28(6), 1508–1511). In contrast, higher molecular weight clusters cannot be converted back into active species under hydroformylation conditions (Yu. B. Kagan, E. V. Slivinskii, V. I. Kurkin, G. A. Korneeva, R. A. Aranovich, N. N. Rzhevskaya, S. M. Loktev, Neftekhimiya (1985), 25(6), 791–797). The formation of clusters is generally the cause of and the first step in the formation of solid rhodium-containing precipitates. It occurs during work-up by distillation, but sometimes also under reaction conditions. Rhodium-containing precipitates deposit on walls of vessels and pipes. This leads to considerable economically disadvantageous catalyst losses and makes regular plant shutdowns and cleaning work necessary in industrial use. Rhodium precipitates have to be recovered by means of a complicated metallurgical route.
Because of the attractiveness of unmodified rhodium as hydroformylation catalyst on the one hand and its instability on the other hand, many processes for its circulation and/or recovery have been proposed.
A series of processes in which removal of the rhodium species from the reaction mixture is carried out by means of solid adsorbents are known. Thus, for example, DE 19 54 315 proposes weakly to strongly basic ion-exchange resins based on polystyrene as adsorbents. According to DE 20 45 416, regeneration of loaded ion-exchange resins can be carried out by treatment with mixtures of lower alcohols, aliphatic amines and water in the presence of oxygen. The rhodium present in the eluate is converted by evaporation and treatment with hydrochloric acid into rhodium chloride hydrate which can be reused as catalyst precursor. WO 02/20451 and U.S. Pat. No. 5,208,194 claim the recovery of rhodium from loaded ion exchangers by incineration of these and isolation of the rhodium as oxide from the ash obtained. In U.S. Pat. No. 4,388,279, salts of metals of groups 1 and 2 of the Periodic Table of the Elements, zeolitic molecular sieves and ion-exchange resins are proposed as adsorbents. WO 01/72679 claims a process for the adsorption of rhodium on activated carbon, polysilicic acids and aluminum oxides at elevated temperature in the presence of hydrogen. The patent EP 0 355 837 describes a process for the adsorption of rhodium on basic ion-exchange resins which are modified with ionically bound organophosphorus ligands. Regeneration of the resin is carried out by elution with a solution containing organophosphorus ligands. WO 97/03938 claims a process for the adsorption of active rhodium species and of impurities on acidic ion-exchange resins. Regeneration is carried out by elution of the impurities with a neutral solvent in a first step and subsequently by elution of the active rhodium species using an acidic solvent. The catalyst which has been recovered in this way is, if appropriate after rehydrogenation, reused in the hydroformylation.
A disadvantage of all the adsorptive processes for the recovery of rhodium is the not satisfactorily solved problem of reliberation of the active species. A person skilled in the art will know that the solvents or solvent mixtures proposed for this purpose are not inert in hydroformylation but lead to secondary reactions. For example, acidic solvents induce the highly exothermic and difficult-to-control aldolization of the aldehydes. Alcohols and amines undergo condensation reactions with aldehydes and thus reduce the product yield. It is therefore absolutely necessary to remove the abovementioned solvents or solvent mixtures before recirculation of the catalyst. This makes the recovery concept extremely technically complicated and expensive. In contrast, adsorption on ion exchangers with subsequent ashing and metallurgical rhodium recovery has attained some industrial importance. This process is technically simple but nevertheless capable of improvement: an expensive basic ion exchanger is used as a consumable material and ashing with subsequent metallurgical work-up of the metal oxides is associated with further extremely complicated process steps.
Also known are a series of processes in which rhodium is extracted from the output from the reactor by means of solutions of various complexing agents and is recirculated to the hydroformylation reactor after it has been liberated again. Thus, for example, rhodium-catalyzed hydroformylation in the presence of protonable nitrogen-containing ligands, extraction of the rhodium complex with aqueous acid, deprotonation and recirculation of the rhodium to the process is known from DE 196 03 201. In DE 4 230 871, the aqueous solution is recirculated directly to the reaction. In EP 0 538 732, extraction of the output from the reactor with aqueous phosphine solution under synthesis gas pressure is claimed. WO 97/03938 claims water-soluble polymers such as polyacrylic acids, maleic acid copolymers and phosphonomethylated polyvinylamines, polyethylenimines and polyacrylamides as complexing agents. EP 0 588 225 claims pyridines, quinolines, 2,2′-bipyridines, 1,10-phenanthrolines, 2,2′-biquinolines, 2,2′,6′,2″-terpyridines and porphyrins, possibly in sulfonated and/or carboxylated form, as complexing agents. However, the complexing agents necessary in aqueous extraction are often expensive and hard to obtain. In addition, these processes involving two additional steps (extraction and catalyst liberation) require an increased engineering outlay.
Furthermore, processes in which rhodium precipitates in the classical work-up of the output from the reactor by distillation are said to be prevented by addition of phosphorus(III)-containing ligands are also known (DE 33 38 340, U.S. Pat. No. 4,400,547). The regeneration or reliberation of the hydroformylation-active rhodium species is carried out by oxidation of the phosphorus(III) ligands. A disadvantage of this process is the continuous stabilizer consumption. The phosphorus(V) compounds formed have to be discharged continually to prevent accumulation in the reactor system. Part of the rhodium in active form is unavoidably discharged too. This process, too, is therefore capable of improvement both technically and economically.
WO 82/03856 claims the distillation of the output from the hydroformylation reactor in the presence of oxygen. In the presence of oxygen, part of the aldehydes formed in the hydroformylation is oxidized to the corresponding carboxylic acids which react with the rhodium species to form soluble rhodium carboxylates. The rhodium carboxylates can be recirculated to the process. A disadvantage of this process is a reduced yield of desired product.
The as yet unpublished patent application DE 102 40 253 describes hydroformylation in the presence of catalysts based on metals of groups 8 to 10 of the Periodic Table of the Elements and modified by phosphorus ligands, with cyclic carbonic esters being used as solvents. The use of unmodified metal complexes of metals of groups 8 to 10 of the Periodic Table is not described.
JP 10-226662 describes a process for the hydroformylation of olefinic compounds in which a rhodium catalyst is used together with a sodium salt of sulfonated triphenylphosphines as cocatalyst, i.e. a modified catalyst is used. The reaction is carried out in the presence of a polar component and a carboxylic acid. The polar component can be, for example, ethylene carbonate. The polar component can be recirculated to the hydroformylation reaction together with the acid and the catalyst. However, the process can be used only for the hydroformylation of terminal olefins, which are comparatively reactive. In the case of internal olefins and especially internal highly branched olefins, the activity of the catalyst is far below that required for industrial uses.
The processes known hitherto for circulation or recovery of rhodium from processes which utilize unmodified rhodium as hydroformylation catalyst are capable of improvement from both a technical and an economic point of view.